Calculate Kp at this temperature for the reaction?

Question

A sample of gaseous SO3 was introduced into an evacuated flask so that the pressure of pure SO3 would be 0.4800 atm at 525 K.
But, SO3 decomposes to gaseous SO2 and O2.
At equilibrium the TOTAL pressure in the flask was measured at 0.6048 atm. Calculate Kp at this temperature for the reaction

SO3(g) ↔ SO2(g) + 1/2 O2(g)

Answer 1

Concentration of any spiece is directly proportional to its partial pressure. Let us assume that the partial pressure of SO2 at equilibrium is X (atm). According to the reaction equation, the partial pressures of SO3 and O2 at equilibrium must be (0.4800 - X) atm and X/2 atm, respectively. Thus:
(0.4800 - X) + X + X/2 = 0.6048
Solving this equation, we get X = 0.2496
Hence Kp = X*(X/2)/(0.4800 - X)
= 0.1352 (atm)